1. Field of the Invention
The present invention relates to a hydrometallurgical process for nickel oxide ore.
More particularly, the present invention relates to a hydrometallurgical process for nickel oxide ore of recovering nickel and cobalt from nickel oxide ore by a high pressure acid leaching that included an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step and a final neutralization step; and which hydrometallurgical process can achieve the tasks of suppressing the abrasion of facilities such as piping and pumps caused by the ore slurry produced from the ore processing step, increasing durability, reducing the amount of a final neutralized residue produced from the final neutralization step, and suppressing the cost and environmental risks by compressing the volume of the tailing dam that stores the leaching residue that will be disposed of, neutralized precipitate, and the like, and also enables separation and recovery of impurity components that can be effectively utilized by recycling.
2. Description of the Related Art
In recent years, as a result of further progress in oligopolization of the rights to mining for mineral resources such as coal, iron, copper, nickel, cobalt, chromium, and manganese, the raw material cost for metal smelting is increasing to a large extent. Therefore, even for metal smelting, development of technologies for using low grade raw materials that have not been hitherto taken into consideration because it is disadvantageous in terms of cost, is underway as a measure for cost reduction.
For example, in regard to nickel smelting, materials having excellent corrosion resistance at a high temperature and a high pressure have been developed. Thus, attention has been paid to a hydrometallurgical process based on a high pressure acid leaching of subjecting nickel oxide ore to acid leaching with sulfuric acid under pressure.
The high pressure acid leaching does not include dry processes such as a reduction process and a drying process, unlike a pyrometallurgical method which is a conventional common smelting method for nickel oxide ore, and is advantageous in terms of energy and cost. Therefore, the high pressure acid leaching will be continuously considered as a promising technology as a smelting method for low grade nickel oxide ore. Accordingly, in order to increase the level of performance as a smelting process, various suggestions have been made mainly on the leaching process at a high temperature under pressure, in connection with an increase in the leaching ratios of nickel and cobalt, solution purification of the leachate, a decrease in the amount of use of the operation materials, and the like.
Meanwhile, regarding a process of utilizing leaching at a high temperature under pressure, for example, there has been suggested a method of recovering valuable metals, such as nickel, cobalt and manganese, from oxide ores containing these metals, the method including the following steps (a) to (c) (see, for example, JP 06-116660 A (Page 1 and Page 2)).
Step (a): Oxide ore that has been slurrified in advance is subjected to leaching at normal pressure under sulfuric acid condition, using a pressurized acid leachate obtained in a step (b) as shown below, and a normal-pressure leachate and a normal-pressure leach residue are obtained.
Step (b): The normal-pressure leach residue obtained in the step (a) is allowed to react with sulfuric acid in an oxidizing atmosphere at a high temperature and a high pressure, and thus a pressurized acid leachate is obtained.
Step (c): A neutralizing agent is added to the normal-pressure leachate obtained in the step (a) to neutralize the leachate, subsequently a sulfurized alkali compound is added thereto, and nickel and cobalt in the leachate are recovered as sulfides.
In this method, the leach rate of nickel from ore is increased by performing two-stage leaching of subjecting an ore slurry to normal-pressure leaching (step (a)), and then the normal-pressure leach residue is subjected to acid leaching under pressure (step (b)). At the same time, the excess acid contained in the leachate of pressurized acid leaching is neutralized by the alkali component contained in the normal-pressure leach residue, and the burden of the neutralization step (step (c)) is reduced.
However, due to the two-stage leaching, there is a problem that the number of facility items increases so that more cost and efforts are needed, and it requires expenses to treat a large amount of a thin solution generated at the time of washing the leach residue.
Thus, in order to solve these problems, there has been suggested a method including the steps (1) to (4) as shown below, as another process of utilizing leaching at a high temperature under pressure (see, for example, JP 2005-350766 A (Page 1 and Page 2)).
(1) Leaching step: Nickel oxide ore is prepared into slurry, sulfuric acid is added thereto, the mixture is stirred at a temperature of 220° C. to 280° C., and thus a leached slurry is formed.
(2) Solid-liquid separation step: The leached slurry obtained in the previous leaching step is washed using multi-stage thickeners, and the leached slurry is separated into a leachate containing nickel and cobalt, and a leach residue.
(3) Neutralization step: The pH of the leachate obtained in the solid-liquid separation step is adjusted to 4 or less using calcium carbonate while suppressing oxidation of the leachate, a neutralized precipitate containing trivalent iron is produced, and the neutralized precipitate is separated into a neutralized precipitate slurry and a mother liquor for nickel recovery.
(4) Sulfurization step: Hydrogen sulfide gas is blown into the mother liquor for nickel recovery obtained in the sulfurization step, sulfides containing nickel and cobalt are produced, and the sulfides are separated from a barren liquor.
Here, an outline of a practical plant based on the technology disclosed in JP 2005-350766 A (Page 1 and Page 2) will be described with reference to the drawings.
FIG. 2 is a smelting process diagram illustrating an exemplary practical plant based on the hydrometallurgical process for nickel oxide ore (JP 2005-350766 A (Page 1 and Page 2)).
In FIG. 2, nickel oxide ore 8 is first mixed with water in (1) ore processing step, subsequently the removal of foreign materials and the adjustment of ore particle size are carried out, and an ore slurry 9 is formed.
Next, the ore slurry 9 is subjected to high-temperature pressure leaching using sulfuric acid in (2) leaching step, and thus a leached slurry 10 is formed.
The leached slurry 10 thus formed is subjected to (3) solid-liquid separation step to be washed in multiple stages, and then the leached slurry is separated into a leachate 11 containing nickel and cobalt, and a leach residue slurry 12.
The leachate 11 is subjected to (4) neutralization step, and is separated into a neutralized precipitate slurry 13 containing trivalent iron hydroxide, and a mother liquor (1) for nickel recovery 14.
The mother liquor (1) 14 is subjected to (5) zinc removal step of adding a sulfurizing agent, and the mother liquor is separated into a zinc sulfide precipitate 15 containing zinc sulfide, and a mother liquor (2) 16 for nickel recovery.
Next, the mother liquor (2) 16 is subjected to (6) sulfurization step, and is separated into a mixed sulfide 17 containing nickel and cobalt, and a barren liquor 18 having nickel and the like removed therefrom. The barren liquor 18 is used as washing water for the leach residue in (3) solid-liquid separation step.
Finally, the leach residue slurry 12 is subjected to (7) final neutralization step together with an excess amount of the barren liquor 18, and the leach residue slurry is neutralized. A final neutralized residue 19 is stored in a tailing dam 20.
A feature of this method lies in that by washing the leached slurry in multiple stages in the solid-liquid separation step, the amount of neutralizing agent consumption and the amount of precipitate in the neutralization step can be reduced; since the true density of the leach residue can be increased, the solid-liquid separation characteristics can be improved; and the process is simplified by performing the leaching step simply by high-temperature pressure leaching. Thus, this method is considered to be advantageous against the method suggested in JP 06-116660.
Furthermore, it is believed that when such a barren liquor is used as the washing liquid used in the solid-liquid separation step, nickel adhering to the leach residue can be leached and recovered using residual sulfuric acid, and repeated use of water can be carried out effectively and efficiently.
Furthermore, when the neutralized precipitate slurry is sent to the solid-liquid separation step, the loss of nickel can be reduced, and therefore, it is believed to be more advantageous.
However, a practical plant adopting this method has the following problems.
(1) Suppression of Abrasion of Facilities
Although nickel oxide ore is conveyed in the form of slurry between various processes, abrasion of the facility materials is markedly accelerated so that there occurs a high frequency of maintenance particularly in facilities such as piping and pumps in the leaching step, and this high frequency serves as a major factor for an increase in the maintenance cost and a decrease in the rate of plant operation.
(2) Reduction of Amount of Final Neutralized Residue
The leach residue obtained in the solid-liquid separation step is combined with excess barren liquor produced from the sulfurization step, and the mixture is made harmless by a neutralization treatment of adding a limestone slurry or a slaked lime slurry thereto.
The final neutralized residue produced from this final neutralization treatment step (hereinafter, may be referred to as final neutralization step) is stored in the tailing dam. However, the final neutralized residue contains, in addition to impurity components such as hematite and chromite in the leach residue, gypsum that is formed by the neutralization treatment so that the final neutralized residue cannot be recycled, and there is a heavy burden of expenses for the construction and maintenance management of the tailing dam.
Under such circumstances, there has been a demand for a solution for the problems described above with regard to the practical plant using a hydrometallurgical process based on the high pressure acid leaching.
Furthermore, in order to solve the problems in an effective and economically efficient manner, it is an effective measure to efficiently separate and recover impurity components that are contained in the ore or leach residue, and it is also demanded to recycle and effectively utilize these impurity components.
Thus, the applicant of the present application has suggested in JP 2010-95788 A a hydrometallurgical process for nickel oxide ore, which includes a step of physically separating and recovering particles containing at least one selected from silica mineral, chromite or silica-magnesia mineral from ore slurry, and a step of physically separating and recovering hematite particles in the leach residue slurry, in a hydrometallurgical process based on a high pressure acid leaching. However, further improvements have been needed for efficient separation and recovery of impurity components contained in ore or leach residue, and recycling of these impurity components that have been separated and recovered.
Under such circumstances, the present invention was achieved in view of the problems of the conventional technologies, and it is an object of the present invention to provide a hydrometallurgical process for nickel oxide ore of recovering nickel and cobalt from nickel oxide ore by a high-pressure acid leaching that includes an ore processing step, a leaching step, a solid-liquid separation step, a neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step; and which hydrometallurgical process can achieve the tasks of suppressing the abrasion of facilities such as piping and pumps caused by the ore slurry produced from the ore processing step, increasing durability, increasing the solid content ratio of the ore slurry, simplifying the facilities of the ore processing step, reducing the amount of a final neutralized residue produced from the final neutralization step, and suppressing the cost and environmental risks by compressing the volume of the tailing dam that stores the leaching residue that will be disposed of, neutralized precipitate, and the like, and also enables separation and recovery of impurity components that can be effectively utilized by recycling.